40 Questions
What is the primary function of the stator in a DC motor?
Generate the magnetic field
Which component of the DC motor is responsible for converting electrical energy into mechanical energy?
Armature
What is the purpose of the commutator in a DC motor?
Switch the current direction in the armature coil
In a large DC motor, what is used instead of permanent magnets to create the stator's magnetic field?
Field coil
What is the role of the yoke in a DC motor's construction?
Provide structural strength to the motor
What is the characteristic of a DC series motor before magnetic saturation of the field?
Parabola
In a DC shunt motor, what is the relationship between armature torque and armature current?
Directly proportional
What is the primary reason a shunt motor should not be started on heavy loads based on the characteristics?
Large current requirement
How is the field winding connected in a DC compound motor?
Part in parallel and part in series
Why does the speed of a shunt motor slightly decrease when the load is increased?
Back EMF decreases
In a DC motor, the magnetic field is provided by:
Permanent magnets
What is the purpose of the commutator in a DC motor?
To transfer electricity to the armature coils
What causes the armature conductors to experience a force in a DC motor?
Magnetic field and current in the armature winding
What is the function of the poles and pole shoe in a DC motor?
To generate a magnetic field
How is the speed of a DC series motor affected?
Proportional to the load current
What is the general relationship between torque and armature current in DC series motors prior to magnetic saturation?
It is cubic
How does the speed of a DC series motor change with an increase in armature current?
Speed decreases
What happens to the speed versus armature current curve of a DC series motor after magnetic saturation is reached?
It becomes a straight line
What is the primary principle on which the construction of a single-phase transformer is based?
Faraday's law
Which material is NOT commonly used in the construction of a transformer core?
Copper
What is the purpose of the Buchholz relay in a single-phase transformer system?
To guard against internal and early faults
What causes the change in color of silica gel crystals used in a single-phase transformer breather?
Absorption of moisture
How does an on-load tap changer differ from an off-load tap changer in a single-phase transformer?
Off-load tap changer requires the transformer to be disconnected from the power supply
What is the role of the explosion vent in a single-phase transformer?
To release excess pressure within the transformer
What is the purpose of the no-load current in a single-phase transformer?
Creates the magnetomotive force for inducing flux
What is the primary current I1’ called due to its phase opposition with the secondary current I2?
Primary Counteract Current
What happens to the direction of the flux when the additional current I’1 is induced?
Flux changes direction
What describes the power factor angle ?1 of the primary side of the transformer?
Angle between V1 and I1'
What does the form factor of 1.11 for a sinusoidal waveform indicate?
Waveform factor
What is the relationship between the RMS values of induced emf in the primary and secondary windings of a transformer?
E1 / E2 = N1 / N2
Which material is recommended to minimize hysteresis loss in a transformer?
Silicon steel
What is the type of loss that can be minimized by constructing the core of a transformer with thin laminations?
Eddy current loss
What is the Power loss known as that is caused by the circulation of eddy currents in a transformer's core?
Eddy current loss
What remains constant in a transformer from no-load to full load, leading to it being known as a constant loss?
Iron loss
What causes copper losses in a transformer?
Ohmic resistance in windings
Which type of loss in a transformer is influenced by the load and hence called variable loss?
Copper loss
What is the formula to calculate the hysteresis loss in a transformer?
Ph = Kh V f Bm2.6
Which loss in a transformer arises due to the alternating nature of the flux in the core, leading to eddy currents and subsequent energy dissipation?
Eddy current loss
What is the reason for using thin laminations in the core of a transformer?
To reduce hysteresis loss
How do copper losses vary in a transformer as compared to iron losses?
Iron losses increase with load variation, unlike copper losses
Learn about DC Motors, an electrical device that converts electrical energy into mechanical energy using Direct Current (DC). Understand how the armature coil interacts with strong permanent magnets to create motion in the motor.
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